WASHINGTON (CNN) -- President Bush said Wednesday he will ask Congress for an additional $600 million to aid victims of the December 26 tsunami that ravaged parts of southern Asia.

That aid would be in addition to the $350 million the United States already has pledged, according to a written statement from the White House.

A 9.0 magnitude earthquake in the Indian Ocean triggered the massive waves, which struck a dozen nations. The disaster killed more than 160,000 people, with Indonesia hit hardest.

"I will seek $950 million as part of the supplemental appropriations request to support the areas recovering from the tsunami and to cover the costs of relief efforts to date," Bush said.

"We will use these resources to provide assistance and to work with the affected nations on rebuilding vital infrastructure that re-energizes economies and strengthens societies."

Bush pledged $350 million on December 31 after facing criticism for first offering $15 million and then raising that to $35 million two days after the disaster.

Andrew Natsios, the administrator of the U.S. Agency for International Development, told reporters Wednesday that the $950 million humanitarian pledge would represent "the most generous and the most extensive in American history for the U.S. government."

Deputy Secretary of Defense Paul Wolfowitz said at the press briefing that some 16,000 U.S. military personnel in the region have delivered more than 10 million pounds of food and provided more than 400,000 gallons of fresh water. He also stressed the diplomatic importance of the relief mission for the United States.

"Above and beyond the humanitarian considerations -- which would be compelling enough -- we have an enormous interest in seeing this succeed," Wolfowitz said, noting Indonesia's status as both an "emerging democracy" and the world's most populous Muslim country.

The White House said the $950 million will include $339 million for reconstruction of infrastructure; $168 million to help victims transition back to their communities; $35 million for early-warning and disaster-mitigation efforts; and $62 million to help plan reconstruction activities and cover the costs of U.S. agencies in the region.

The total also includes $346 million to cover money already spent by the USAID and the Defense Department, the White House said, and an unspecified sum may also be used to cover debt deferment for tsunami-affected countries.

Former presidents thanked

President Bush in January tapped former presidents Bill Clinton and George H.W. Bush to help encourage private-sector financial support for tsunami relief.

On Wednesday, the president said he is grateful for the fund-raising efforts by his father and Clinton. And he expressed appreciation "to all of those who have donated money to help those in need."

The White House said estimates place private-sector donations toward tsunami relief efforts at more than $700 million.

Clinton and the elder Bush will visit tsunami-affected countries this month, the White House said, including Indonesia, Sri Lanka, Thailand and the Maldives.

Last week, the United Nations announced Clinton will serve as the world body's envoy for tsunami reconstruction efforts. (Full story)

U.N. Secretary-General Kofi Annan believed "no one could possibly be better qualified for this task," a spokesman said.